Association between cMIND diet and hypertension among older adults in China: a nationwide survey

Background Existing research indicates that the Mediterranean diet has a positive impact on preventing and treating hypertension. However, its specific effect on hypertension among elderly Chinese individuals is unclear. Aims The objective of this research was to explore the association between the Chinese version of the Mediterranean-DASH Intervention for Neurodegenerative Delay (cMIND) diet and hypertension among elderly Chinese individuals, aiming to offer novel strategies for alleviating the burden of hypertension in this demographic. Methods In this study, we used cross-sectional data published in 2018 by the China Longitudinal Health and Longevity Survey (CLHLS) to develop a binary logistic regression model to investigate the correlation between cMIND diet and hypertension in a Chinese elderly population. Restricted cubic spline was used to test for linear associations, and further subgroup analyses were performed to test for interactions. Results In total, 7,103 older adults were included in the study, with a prevalence of hypertension of 39.0%. When the cMIND diet score was used as a continuous variable, a significant protective effect against hypertension was present (OR = 0.955, 95% CI:0.923–0.988, p = 0.008); when used as a categorical variable, this protective effect was still present at higher levels (compared to lower levels) of the cMIND diet (OR = 0.869, 95% CI: 0.760–0.995, p = 0.042). Discussion Although the Mediterranean diet has great potential to reduce the chance of hypertension, it should also consider the effect on the Chinese population. The results of this study provide new ways to reduce the disease burden of hypertension in Chinese older adults and improve quality of life in later life. Conclusion The cMIND diet can considerably reduce the risk of hypertension among older adults in China. Supplementary Information The online version contains supplementary material available at 10.1007/s40520-024-02842-3.


Introduction
A global report on hypertension, published by WHO in 2023, states that over one billion people are at risk of hypertension and its associated complications [1].Global Burden of Disease 2019 study shows that the average prevalence of cardiovascular disease was 77-80% among individuals aged 60 to 80 and more than 85% in people over 80 years old [2].The results of a study showed that the age-prevalence of hypertension is nearly 90% [4].Hypertension stands as a prevalent chronic illness among older adults in China, significantly contributing to cardiovascular disease, which remains the primary cause of mortality globally [5,6].Hypertension usually causes complications encompassing cardiovascular disease (CVD), stroke, and kidney dysfunction, resulting in a diminished quality of life and shorter life expectancy [7].A study on the Global Burden of Disease Study 2017 found that a significant contribution to stroke-related deaths (69%), ischemic heart disease fatalities (54%), and chronic kidney disease mortalities (43%) was traced back to hypertension [8].Extensive research has revealed a robust correlation between the development of hypertension and a variety of risk factors, such as population aging, family history, obesity, smoking, alcohol consumption, and stress [4,[9][10][11][12][13].The Global Sustainable Development Goals (SDGs) plan released by the World Health Organization mentions a projected 33% reduction in noncommunicable diseases, including hypertension, by 2030 [14].Therefore, it is urgent to find protective factors that can effectively reduce the probability of developing hypertension.De Pergola G. et al. concluded that a healthy lifestyle represents a cornerstone approach to reducing hypertension, and dietary patterns are the most influential variable on blood pressure [15].DASH (Dietary Approaches to Stop Hypertension) dietary pattern is effective in controlling blood pressure levels in many studies and has substantial advantages in the management of hypertension [16][17][18].In addition to the DASH diet, scholars have also widely noted the role of the Mediterranean diet in reducing hypertension.
The Mediterranean dietary pattern, stemming from the cultures bordering the Mediterranean Sea basin, represents a distinctive eating habit characterized by an abundance of fruits, vegetables, whole grains, legumes, nuts, and seeds, coupled with moderate consumption of dairy products, poultry, and fish while limiting the intake of red meat and sweets [19].The Mediterranean diet emphasizes monounsaturated fats and polyphenols, which protect the heart and reduce atherosclerosis and cardiovascular diseases [20,21].A study showed that the Mediterranean diet is a healthful dietary model that minimizes the risk of non-communicable diseases [22].Extensive research indicates that adopting the Mediterranean diet reduces the probability of developing hypertension [23][24][25].However, due to the many differences in dietary patterns between China and the West, the existing Mediterranean dietary patterns are not entirely suitable for China with its diverse dietary culture [26].In recent years, scholars have actively conducted research on the correlation between the Mediterranean diet and chronic illnesses in China and developed a MIND diet (including more whole grains and less refined flour or rice) suitable for the Chinese population (the Chinese version of the Mediterranean-DASH Intervention for Neurodegenerative Delay, cMIND) [27][28][29][30][31][32].Existing studies have shown that in the Chinese elderly population, the Mediterranean diet significantly reduces the probability of developing chronic illnesses such as cognitive impairment (CI), age-related macular degeneration, and cardiovascular disease [27,31,33].
Nevertheless, the association between the Mediterranean diet and hypertension among Chinese older adults remains unknown.Further research evidence of its correlation is imperative to gain a comprehensive understanding of the influence of the Mediterranean dietary pattern on hypertension [15].Hence, the objective of this research was to explore the association between the cMIND diet and hypertension among elderly Chinese individuals, aiming to offer novel strategies for alleviating the burden of hypertension in this demographic.

Participants and process
The data utilized in this research was derived from the Chinese Longitudinal Healthy Longevity Survey (CLHLS).Launched in 1998, this project employs a multi-stage stratified sampling approach to identify participants, offering insights into the health conditions and well-being of elderly individuals aged 65 and above across 23 provinces in China.Data were collected one-on-one by trained professionals to ensure a representative and reliable sample.Subjects signed an informed consent form to agree to the survey, and the project was approved by the Biomedical Ethics Committee of Peking University, China (IRB00001052-13074).
In this study, we used cross-sectional data published in 2018 to explore the relationship between the cMIND diet and hypertension, and the inclusion criteria for the study population were (i) age ≥ 65 years and (ii) no missing data for covariates and critical variables.The data cleaning procedure is depicted in Fig. 1.

Assessment of cMIND diet
Huang X et al. developed the cMIND diet scale for the Chinese population based on the MIND diet scale and CLHLS food frequency questionnaire and assessed its reliability in the population [29].cMIND diet consists of 12 food items: fresh vegetables, mushrooms/algae, fresh fruits, fish, soya beans, nuts, garlic, tea, sugar/sweets, type of staple food, quantity of staple food, and cooking oil.Three items, staple food type, staple food quantity, and cooking oil, were scored as 0 or 1, and the remaining nine items were scored as 0, 0.5 or 1.The cMIND diet adherence was evaluated on a 0-12 scale, where a higher score signifies greater conformity to the diet.In this study, the cMIND diet scores were categorized into three groups according to quantiles: low (0-4), medium (4.5-5.5), and high (6)(7)(8)(9)(10)(11)(12), and assigned the values of 0, 1, and 2, respectively.

Assessment of hypertension
This study designated hypertension as (1) a self-reported history of hospital-diagnosed hypertension; (2) systolic blood pressure ≥ 140 mmHg or diastolic blood pressure ≥ 90 mmHg.Two blood pressure measurements were taken during the survey, with an interval of at least 1 min between measurements, and the average of the two systolic and diastolic blood pressures was taken.A participant was classified as hypertension if either criterion was fulfilled [34,35].

Covariates
Based on the results of previous studies [31,36,37], we controlled for confounders in terms of basic characteristics, lifestyle, and chronic diseases of the study population to minimize the impact on the results, including gender (male or female), age (65-79 or ≥ 80), place of residence (urban or rural), living arrangement (living with family, living alone or in an institution), years of education (0, 1-6 and ≥ 7 years), economic status (bad, average or good), marital status (unmarried or married), BMI (< 18.5, 18.5-23.9,or > 23.9), and dichotomous variables (yes or no): smoking, alcohol, exercise, diabetes mellitus, cardiovascular disease, and CI.(As shown in Table S1 of the supplementary information) CI was assessed on the MMSE scale of the CLHLS, which comprises 24 questions in five categories: general ability, reaction, attention and calculation, recall and language, and comprehension and self-coordination.In general ability, the question "In one minute, name the things that a person can eat" scored 7 points (< 7 counts as a raw score, ≥ 7 counts as 7 points), and in evaluating the remaining questions, a mark of 1 point was awarded for a precise response.In contrast, an inaccurate response or failure to complete the question resulted in 0 points.The cognitive function of older adults was evaluated on a scale ranging from 0 to 30, wherein a higher score indicated superior cognitive performance.A threshold of 24 points was established as a benchmark, and a score of more than 24 points was defined as cognitively normal, with a value of 0; a score equal to or less than 24 points was defined as cognitively impaired, with a value of 1 [38].

Statistical analysis
Categorical variables were characterized by frequencies and percentages (n, %), while continuous variables that adhered to normal distribution were summarized with the mean and When cMIND diet was used as a categorical variable, both medium and high levels of cMIND diet reduced the risk of hypertension in model 1 (medium level: OR = 0.892, 95% CI: 0.797 to 0.997, p = 0.045; high level: OR = 0.777, 95% CI: 0.689-0.875,p < 0.001); in model 2 and model 3, which further controlled for covariates, this protective effect persisted at higher levels of the cMIND diet (model 2: OR = 0.835, 95% CI: 0.736-0.947,p = 0.005; model 3: OR = 0.869, 95% CI: 0.760-0.995,p = 0.042).As shown in Fig. 2, the restricted cubic spline curve results demonstrated a statistically significant correlation between cMIND diet and hypertension in older adults in China (p < 0.05).Besides, the cMIND diet score revealed a linear trend with the prevalence of hypertension (p for non-linear = 0.212).

Subgroup analysis
Further subgroup analysis based on Model 3 covariates found that the correlation between the cMIND diet and the prevalence of hypertension was statistically significant in people < 80 years old, females, urban residents, the married, non-smokers, non-drinkers, exercisers, those without diabetes, those without cardiovascular disease, and those without CI.No significant interaction was found in the subgroup analysis, as shown in Fig. 3.

Sensitivity analysis
As shown in Table S2 of the supplementary information, two sensitivity analyses were performed utilizing model 3 as the basis to ensure the robustness of the results: (i) older adults with diabetes and heart disease were excluded; (ii) older adults with CI (MMSE ≤ 24) were further excluded.The findings indicated that the protective effect of the cMIND diet on hypertension in older adults is still present regardless of whether the cMIND diet is a continuous or categorical variable.

Discussion
Utilizing 2018 cross-sectional data from the CLHLS database, we found that the cMIND diet significantly reduced the probability of developing hypertension among older Chinese adults, and restricted cubic spline analysis showed a significant linear relationship.Further subgroup analysis found that the correlation between cMIND diet and hypertension was statistically notable in people < 80 years of age, females, urban residents, the married, non-smokers, nondrinkers, exercisers, those without diabetes, those without the standard deviation (M ± SD). χ2 tests and t-tests were introduced to compare disparities between participants with varying demographic attributes.We further developed three logistic regression models to analyze the correlation between cMIND diet (considering both continuous and categorical conditions) and hypertension.Model 1 did not control for any factors; model 2 controlled for sex, age, and BMI; and model 3 further controlled for place of residence, living arrangements, years of education, economic status, marital status, smoking, alcohol, exercise, diabetes, cardiovascular disease, and CI.
Employing RCS, we examined the presence of a nonlinear association between the cMIND diet and hypertension.In addition, we conducted subgroup analyses and interaction analyses by gender, age, place of residence, marital status, smoking, alcohol, exercise, diabetes, cardiovascular disease, and CI to test for the modified effects of these variables.Finally, sensitivity analyses demonstrated the robustness of the results.Statistical analyses were conducted using SPSS 26.0 and R 4.3.0,and a significance level of p < 0.05 was established.

The characteristics of study participants
In total, 7,103 samples were incorporated in this research, of which the incidence of hypertension in the demographic was 39%.As shown in Table 1, the number of women (53.75%) was higher than that of men (46.25%), and the proportion of women suffering from hypertension (50.51%) was higher than that of men (49.49%).The older adults aged over 80 accounted for 57.81%, of which 58.27% were hypertension.The results of χ² analysis showed statistically significant differences between different cMIND diets, gender, living arrangement, economic status, smoking, alcohol, BMI, diabetes, cardiovascular disease, CI and prevalence of hypertension.The t-tests conducted on two independent samples revealed significant variations in cMIND diet scores among those with or without hypertension.

Association between cMIND diet and hypertension
As depicted in Table 2, the logistic regression model found that when cMIND diet was used as a continuous variable, in model 1 without controlling for any variable, the risk of hypertension was reduced by 0.926 times for every one unit increase in the score of cMIND diet (OR = 0.926, 95% CI:0.899-0.954,p < 0.001); in models 2 and 3, which further controlled for covariates, the protective effect was reduced but still significant (model 2: OR = 0.945, 95% dietary regimens exhibiting effectiveness in reducing such a condition: the DASH diet, the Mediterranean diet, the low-sodium diet, the vegetarian diet, and the combination diet [20].Among them, the Mediterranean diet has received much attention for its great potential to reduce the chance of hypertension.A comprehensive assessment of substantial epidemiological data revealed that adherence to the Mediterranean diet leads to a marked decrease in blood pressure levels among patients with hypertension [23]; Song Y et al. concluded that the Mediterranean diet has practical cardiovascular disease, and those without CI, and the interaction was nonexistent.The sensitivity analysis results further proved the robustness of the results.The American Heart Association's recommendations emphasize the pivotal role of dietary modifications in hypertension prevention and management, highlighting that adherence to healthy dietary patterns can drastically lower the risk of cardiovascular disease [39].Scholars have long been interested in dietary approaches that can mitigate the probability of developing hypertension, with five significant  our study represents a novel exploration into the association between the cMIND diet and hypertension among elderly individuals in China.The pathogenesis of hypertension is complex and varied and has long been a concern of scholars.As early as the 1950s, Irving Page proposed a complete theory of the pathogenesis of arterial hypertension, namely the Page mosaic theory [44].As of today, there are two primary pathophysiological pathogenesis of hypertension -increased peripheral resistance and increased cardiac output.Elevated blood pressure in humans causes structural remodeling of blood vessels and rearrangement of vascular smooth muscle cells, resulting in reduced lumen diameter, hypertrophy of blood vessels, and increased vessel wall thickness [45].In recent years, the treatment pattern of hypertension has changed from the initial pharmacological treatment to the present day's equal emphasis on pharmacological treatment and value in both primary and secondary preventative measures against hypertension and that it is a new anti-hypertension dietary pattern [34]; Motamedi A et al. explored the chance of developing hypertension in Iranian adults and found that consistently observing the Mediterranean diet helps to prevent hypertension [24].Apart from this, single foods in the typical Mediterranean dietary pattern have been confirmed by many studies to have a blood pressure-lowering effect, such as fresh vegetables, fruits, coarse grains, green tea, and other foods [40][41][42][43].The dietary pattern used in this study is the Chinese version of the MIND diet based on traditional Mediterranean food by Hang X et al.It is widely reliable and representative of the Chinese population [29].The cMIND diet, tailored to the dietary customs and geographic specifics of China, serves as an economical dietary model that fosters health and nutritional balance for the elderly population in the country [30].According to the available studies, observing the MIND diet can also improve the occurrence of CI [65,66]. Hypertension patients in China account for about 1/5 of the world's patients, and there are three lows in the management and control of hypertension (low awareness rate, low treatment rate, and low control rate), which further increases the healthcare burden of cardiovascular diseases in China [67].The Mediterranean diet has been widely used in China in recent years, but the opportunities for Chinese older adults to obtain and adhere to it are limited [68].Given this, it may be necessary for various government departments and health practitioners to carry out health education to encourage older adults in China to adopt the cMIND dietary pattern.

Conclusions
The study demonstrated that the cMIND diet significantly reduced the risk of hypertension among Chinese older adults, with a significant dose-response relationship.Further subgroup analyses demonstrated the variability of this association between different populations, and finally, sensitivity analyses ensured the robustness of the findings.This study's findings indicate the potential of the cMIND diet in deterring hypertension in elderly Chinese individuals, thereby justifying further extensive research to solidify this correlation and offer innovative methods to reduce the hypertension burden among the senior population.

Limitations
Despite being the initial investigation into the association between the cMIND diet and hypertension among elderly Chinese individuals, the current study does possess certain limitations.Firstly, as a cross-sectional study, the causal relationship between the cMIND diet and hypertension could not be inferred.Secondly, the questionnaire was filled out based on self-report from the study participants, which may have biased information.Finally, hypertension is an intricate, multi-factorial chronic illness, with genetic predisposition serving as a significant intervening variable.Still, there was no information in the questionnaire related to the genetics of hypertension, which should be further included in future studies to explore the effect of genetic factors.
lifestyle interventions, with a particular emphasis on nutritional changes.This study first concluded that the cMIND diet could significantly lower the chance of developing hypertension among Chinese older adults, suggesting that the cMIND dietary pattern could be considered an intervention to decrease the incidence of hypertension among them.Estruch R et al. suggested that the mechanisms of action of Mediterranean dietary interventions include promoting vasodilatation, improving endothelial function, decreasing fluid retention, and attenuating oxidative stress [46].The Mediterranean diet emphasizes unsaturated fats and polyphenols, which can improve the function of the vascular endothelium and help control blood pressure [19].For example, olive oil and fresh fruits and vegetables synergistically relax the blood vessels, thus lowering blood pressure [40,47,48]; monounsaturated fats and polyunsaturated fats found in nuts and fish have been associated with a reduction in blood pressure as well [49,50].Excessive sodium intake causes sodium retention, which in turn increases blood pressure [51,52].The pathogenesis of hypertension involves oxidative stress, which arises from an imbalance between the generation of reactive oxygen and nitrogen species and the antioxidant defense system, resulting in inflammation and subsequent vascular injury [53][54][55][56][57]. Fresh fruits and vegetables and plant sterols have been found to counteract oxidative stress and reduce vascular damage [58].
After stratifying participants by gender, age, place of residence, marital status, smoking, alcohol, exercise, diabetes, cardiovascular disease, and CI, the findings revealed that the correlation between cMIND diet and hypertension was statistically remarkable for people < 80 years of age, females, urban residents, the married, non-smokers, non-drinkers, exercisers, those without diabetes, those without cardiovascular disease, and those without CI.A study among married couples in India found that the prevalence of hypertension in males and females was 29.1% and 20.6% respectively.If the spouse suffered from hypertension, the study subjects were more likely to have hypertension [59].In Nigeria, the chance of developing hypertension among those who are married is notably greater compared to individuals who are not married [60], which may be due to the influence of spouses' similar eating habits and lifestyles [61].Alcohol consumption and smoking often co-exist, and the average alcohol consumption of men is usually higher than that of women [12,62].Alcohol consumption can lead to vasoconstriction and increased heart rate, while smoking can produce oxidative stress and endothelial dysfunction, all of which significantly enhance the likelihood of hypertension [11,63].Furthermore, the association linking hypertension, dementia, and cognitive decline has been unequivocally established [64].Studies have found that the MIND diet can improve language recognition, memory, and attention, and

Fig. 2
Fig. 2 Restricted cubic spline for testing the hypothesis of non-linear correlation between cMIND diet and hypertension

Table 2
Association of cMIND diet with hypertension among Chinese older adults Notes: Mode1 without controlling for any variable; Model 2 controls for Sex, Age, BMI; Model 3 further controls for Residence, Living arrangements, Education, Economic status, Marital status, Smoking, Drinking, Exercise, Diabetes, Cardiovascular disease and CI